Field of the Invention
This invention broadly relates to a process for preparing aliphatic alcohols from synthesis gas and, more particularly, to an improved process in which a zeolite-containing heavy metal oxide catalyst is employed to effect the hydrogenation of carbon monoxide to produce a mixture of lower aliphatic alcohols. This invention also relates to a method of preparing zeolite-containing catalysts which may be useful in the above process.
Lower aliphatic alcohols have been proposed as octane enhancers or as a replacement for gasoline in fueling internal combustion engines. Certain mixtures of lower aliphatic alcohols have the EPA approval for use and are currently being marketed in the United States. The lower aliphatic alcohols can be produced from domestically available non-petroleum sources and the use of thse alcohols in fuel compositions can serve to lessen the nation's dependence on foreign sources of crude oil and petroleum products.
Hydrogen and carbon monoxide or synthesis gas, a mixture of hydrogen and carbon monoxide, can be reacted to form a mixture of lower aliphatic alcohols. The synthesis gas feedstream can be produced from such non-petroleum sources as coal and biomass in well known partial oxidation reactions.
Numerous catalytic processes have been studied in attempts to provide a viable process for the production of aliphatic alcohols from synthesis gas. The early efforts were primarily directed to the production of methanol. More recently, attention has been directed to the production of higher aliphatic alcohols or a mixture of higher aliphatic alcohols with methanol. Such a mixture is highly suitable as an octane enhancing component for motor fuel and as a substitute for tetraalkyl lead additives in motor fuel.
A major problem with the synthesis gas to alcohol conversion process is the occurrence of competing reactions constantly taking place on the surface of the catalyst. Thus, even when the desired product is formed on the catalyst, some of this product may undergo further reactions with adverse effects on the yield of the desired product. It is evident that if some means could be provided for reducing or minimizing competing reactions on the catalyst surface, then improved yields of the desired product might be obtained. In accordance with this invention, a decrease in the number of surface acid sites is achieved by treatment with a thermally stable base or derivative thereof. This procedure reduces the dehydration of product alcohols on the catalyst's acid sites and this results in improved productivity and selectivity.